The objective of this research project is to further our understanding of the regulation of the formation of histamine (HA) and the action of this putative neurotransmitter. HA has been implicated in such wide-ranging and important clinical phenomena as depression, hypertension, and withdrawal from narcotics. Therefore, it is important to expand our knowledge of the basic biochemistry, physiology and pharmacology of this putative neurotransmitter in order to have the potential to be clinically more effective in managing these conditions. This research project will utilize biochemical, neurobiological and pharmacological methodology to explore the regulation and action of brain HA. The primary pathway for HA biosynthesis is via the decarboxylation of Lamda-histidine (HIS) by the specific enzyme Lamda-histidine decarboxylase (HDC). A secondary source of HA is the conversion of N-acetylhistamine to HA by N-acetylhistamine deacetylase (NAcHAD). Neurotransmitter synthesis is often regulated by the synthetic enzyme or by the high affinity uptake of the precursor. Since very little is known about HIS uptake and NAcHAD activity in brain and since they may play significant roles in the regulation of HA synthesis, we will initially characterize HIS uptake and NAcHAD by determining their kinetic parameters such as Vmax and Km. Next we will establish their subcellular and regional localizations in brain followed by studies of their ontogenetic appearance in rats and guinea pigs. In addition, purification of NAcHAD will be accomplished. Antibodies to NAcHAD will be produced and characterized with a long-range goal of using them for cytochemical localization studies. Subsequently, we will use various lesioning techniques and pharmacological manipulations to alter the activity of HA neurons in vivo and to examine the effects on HIS uptake, HDC, and NAcHAD. When chronically altering the histaminergic neuronal systems either by lesions or drug treatments, we will also examine brain tissues for changes in HA-receptor binding and HA-sensitive adenylate cyclase which has been shown to be inhibited by structurally diverse drugs with a common clinical antidepressant property.